Astronomers have captured detailed images of a star other than the Sun for the first time, revealing the movement of gas bubbles on its surface. The discovery offers a fascinating insight into stellar evolution and could help us understand the future of our own Sun.
An international team of astronomers has achieved a technical feat by observing R Doradus, a red giant star located about 180 light-years from Earth. Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, they were able to follow the movement of gigantic bubbles of hot gas on the star’s surface.
The images obtained show gas bubbles 75 times larger than the Sunappearing on the surface of R Doradus and then plunging into its interior. The process, called convection, plays a vital role in transporting energy and chemical elements within stars.
Wouter Vlemmings, professor at Chalmers University of Technology in Sweden and lead author of the study, said: “This is the first time that the bubbling surface of a real star can be shown in such detail.»
ALMA (ESO/NAOJ/NRAO)/W. Vlemmings et al.
R Doradus is particularly interesting because its mass is similar to that of the Sun. It therefore represents a model of what our star will look like in about 5 billion years, when it becomes a red giant. Theo Khouri, a researcher at Chalmers and co-author of the study, explains: “With ALMA, we were not only able to see convective granules directly, but also to measure their speed of movement for the first time.»
The observations revealed that the granules on the surface of R Doradus move on a monthly cycle, which is faster than scientists would have predicted based on how convection works in the Sun. Prof. Vlemmings adds: “We don’t yet know the reason for the difference. It seems that convection changes as a star ages, in ways we don’t yet understand.»
The breakthrough would allow new observations of distant stars. Behzad Bojnodi Arbab, a doctoral student at Chalmers involved in the study, is already considering the use of future telescopes such as those at the SKA Observatory in South Africa and Australia.
He says: “With the SKA telescopes, we will be able to obtain high-resolution observations of R Doradus’ upper atmosphere. We want to see something we haven’t been able to observe yet: how the star’s bubbles might help create its dusty wind.»
R Doradus observations allow astronomers to better understand the physical processes at work in old stars. They provide valuable information on how chemical elements are transported through stars and dispersed in space, contributing to the formation of new stars and planets.
By directly observing phenomena on a star other than the Sun, scientists can refine their models of stellar evolution and improve our understanding of the life cycle of stars.
Behzad Bojnordi Arbab underlines the importance of the study: “It is spectacular that we can now directly image details on the surfaces of stars so distant, and observe physics that until now was only observable in our Sun.»
The detailed observation of R Doradus represents a breakthrough in our understanding of red giant stars. It offers a unique insight into the possible future of our Sun and the complex processes that govern stellar evolution. As new and more powerful telescopes come into service, our knowledge of the Universe and our Sun’s place in it will continue to deepen. Future observations promise to reveal more secrets about the dynamics of stars and their role in the cosmic ecosystem.
* Convection bubbles have been observed in detail on the surface of stars before, notably with the PIONIER instrument on ESO’s Very Large Telescope Interferometer. But the new ALMA observations make it possible to follow the bubbles’ motion in a way that was not possible before.
Image caption: This wide-field view, created from images from the Digitized Sky Survey 2, shows the region around R Doradus, the bright orange star at the centre. The star’s surface was recently imaged in detail using the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner. Credit: ESO/Digitized Sky Survey 2. Acknowledgements: Davide De Martin
This research was presented in a paper titled “One month convection timescale on the surface of a giant evolved star” forthcoming in Nature (doi:10.1038/s41586-024-07836-9).
The research team consists of W. Vlemmings (Chalmers University of Technology, Sweden [Chalmers]), T. Khouri (Chalmers), B. Bojnordi (Chalmers), E. De Beck (Chalmers), and M. Maercker (Chalmers).
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomical facility, is a partnership between ESO, the National Science Foundation (NSF) of the United States and the National Institutes of Natural Sciences (NINS) of Japan, in cooperation with the Republic of Chile.
